Conceptual Physical Science Ch 3
38) When Freddy Frog drops vertically from a tree onto a horizontally-moving skateboard the speed of the skateboard A) decreases. B) increases. C) neither decreases nor increases
. Answer: A
11) A 2500-N pile driver ram falls 10 m and drives a post 0.1 m into the ground. The average force on the post is A) 2500 N. B) 25
000 N. C) 250,000 N. D) 2,500,000 N., Answer: C
1) A machine puts out 100 W of power for every 1000 W put into it. The efficiency of the machine is A) 10%. B) 50%. C) 90%. D) 110%. E) none of the above
Answer: A
1) Whereas impulse involves the time that a force acts work involves the A) distance that a force acts. B) time and distance that a force acts. C) acceleration that a force produces.
Answer: A
10) Bronco's speed increases after he dives from a hovering helicopter. Relative to an observer in the helicopter Bronco's momentum A) also increases. B) remains unchanged. C) decreases.
Answer: A
10) Lifting a 100-N load with 50 N of force lifts it A) half as high. B) as high. C) twice as high.
Answer: A
11) Two identical freight cars roll without friction towards each other on a level track. One car rolls at 2 m/s and the other car rolls at 1 m/s. After the cars collide they couple and roll together with a speed of A) 0.5 m/s. B) 0.33 m/s. C) 0.67 m/s. D) 1.0 m/s. E) none of the above
Answer: A
11) What is the speed of a 4-kg ball with a momentum of 12 kg∙m/s? A) 3 m/s B) 4 m/s C) 12 m/s D) 48 m/s E) none of the above
Answer: A
12) A clerk can lift containers a vertical distance of 1 m or roll them up a 2-m-long ramp to the same elevation. With the ramp the applied force needed is A) half as much. B) twice as much. C) the same.
Answer: A
13) According to the impulse-momentum relationship Ft = change in mv a falling bungee jumper has momentum which is reduced by the force F exerted by the bungee cord. If v is the speed of the jumper then m in the equation is the mass of the A) jumper. B) cord. C) ground below. D) none of the above
Answer: A
15) When wind encounters a wind turbine that produces energy wind speed on the downside of the blades is A) slowed. B) speeded up. C) not affected.
Answer: A
16) Two billiard balls having the same mass roll toward each other at the same speed. What is the net momentum of the two-ball system? A) 0 kg∙m/s B) 10 kg∙m/s C) not enough information
Answer: A
17) An object that has kinetic energy must be A) moving. B) falling. C) at an elevated position. D) at rest. E) none of the above
Answer: A
18) You throw a golf ball at a massive bowling ball at rest and the golf ball bounces backward from it. After the bounce compared with the golf ball the bowling ball has more A) momentum but less kinetic energy. B) kinetic energy but less momentum. C) momentum and more kinetic energy. D) less momentum and less kinetic energy. E) not enough information
Answer: A
19) If a monkey floating in outer space throws his hat away the hat and the monkey will both move A) away from each other but at different speeds. B) away from each other at the same speed. C) a short distance and then slow down. D) a short distance and then gain speed. E) quickly to a stop.
Answer: A
2) A ball rolling down an incline has its maximum potential energy at A) the top. B) a quarter of the way down. C) half-way down. D) the bottom.
Answer: A
2) A heavy truck and a small car roll down a hill at the same speed and need to stop in the same amount of time. Compared with the force to stop the car the force needed to stop the truck is A) greater. B) smaller. C) the same.
Answer: A
2) The unit kilowatt-hour is a unit of A) energy. B) momentum. C) power. D) time.
Answer: A
21) A melon is projected into the air with 100 J of kinetic energy in the presence of air resistance. When it returns to its initial level its kinetic energy is A) less than 100 J. B) more than 100 J. C) 100 J. D) need more information
Answer: A
22) The greater efficiency achieved with the curved blades of a Pelton wheel is due to A) bouncing. B) greater time of water impact. C) rotational momentum. D) divided impulse.
Answer: A
3) If you push for an hour against a stationary wall you do no work A) on the wall. B) at all. C) both of these D) none of the above
Answer: A
30) Recoil is noticeable if we throw a heavy ball while standing on a skateboard. If instead we go through the throwing motion but hold onto the ball without friction effects our net recoil will be A) zero. B) the same as before. C) small but noticeable.
Answer: A
37) Two identical gliders slide toward each other on an air track. One glider moves at 1 m/s and the other glider moves at 2 m/s. They collide stick and move at A) 1/2 m/s. B) 1/3 m/s. C) 1/6 m/s. D) 3/4 m/s. E) 1.5 m/s.
Answer: A
4) If you push an object twice as far while applying the same force you do A) twice as much work. B) four times as much work. C) the same amount of work.
Answer: A
4) The ultimate source of energy from fossil fuels is the A) Sun. B) radioactivity in Earth's interior. C) photosynthesis process. D) natural processes in Earth's interior.
Answer: A
5) A ball is projected into the air with 900 J of kinetic energy that is transformed to potential energy at the top of its trajectory. When it returns to its original level after encountering air resistance its kinetic energy is A) less than 900 J. B) more than 900 J. C) 900 J. D) not enough information
Answer: A
8) The most underlying feature of machines is A) energy conservation. B) that energy input always equals energy output. C) that power input always equals power output. D) all of the above E) none of the above
Answer: A
8) When you simultaneously drop a light tennis ball and a heavy bowling ball they hit the floor A) at the same speed. B) with the same force. C) with the same momentum. D) all of the above E) none of the above
Answer: A
8) Which requires more work on the brakes of a car? A) slowing down from 100 km/h to 70 km/h B) slowing down from 70 km/h to a stop C) equal amounts of work for either
Answer: A
9) The fuel most likely to power tomorrow's scooters forklifts and busses is A) hydrogen. B) helium. C) lithium.
Answer: A
9) When bullets are fired in a forward direction from a fighter aircraft the momentum of the aircraft A) decreases. B) is unchanged. C) increases.
Answer: A
9) When you can't escape being hit by a fast-moving object you'll suffer a smaller force if the collision time is A) long. B) short. C) the same way either way
Answer: A
2) An unfortunate bug splatters on the windshield of a moving car. Describe the forces impulses momentum changes and accelerations of both the bug and the car.
Answer: According to Newton's third law the force of collision will be the same on both the bug and the car but will act in opposite directions. The time during which the force acts is the same on both,so the impulses on the bug and the car will be equal in magnitude but opposite in direction. This means that each will undergo equal and opposite changes in momentum. It is important to stress that the momentum of car and the bug are not the same but they change by the same amount! The car loses as much momentum as the bug gains in the collision. Because of the small mass of the bug its acceleration will be very large. Because of the large mass of the car its acceleration (deceleration) will be unnoticeable.
6) At the edge of a cliff you throw one ball downward and another ball upward at the same speed. Which will hit the ground faster? Does direction of the thrown ball make a difference? Explain.
Answer: According to the conservation of energy for the same initial speed the initial kinetic energy is the same—regardless of the direction the ball is thrown. Thrown from the same height means that its initial potential energy is the same so its total energy is the same for all directions all of which is converted to kinetic energy when the ball hits the ground below. This means the ball will have the same speed in all cases. However the upward and downward thrown balls land at different times. Another story.
1) In raising a 5000-N piano with a pulley system for every 1 m of rope pulled down the piano rises 0.1 m. Ideally this means the force needed to lift the piano is A) 50 N. B) 500 N. C) 5000 N. D) not enough information
Answer: B
1) It is correct to say that impulse is equal to A) momentum. B) the change in momentum. C) the force multiplied by the distance the force acts. D) all of the above E) none of the above
Answer: B
1) Which has the greater kinetic energy? A) a car traveling at 30 km/h B) a car of half the mass traveling at 60 km/h C) both the same D) need more information
Answer: B
10) Hydrogen like electricity is A) an energy source. B) not an energy source. C) a source of both thermal and electric power.
Answer: B
11) Although perpetual motion is the natural order of things in the universe A) it follows that machines can operate and do work by perpetual motion. B) no perpetual-motion device that multiplies energy exists. C) both of these are false statements
Answer: B
11) It takes 40 J to push a large crate 4 m across a floor. The force exerted on the crate is A) 4 N. B) 10 N. C) 40 N. D) 160 N. E) 1600 N.
Answer: B
11) The order in which solar energy is converted to the kinetic energy of an automobile is A) photocells electrolysis motor fuel cells kinetic energy. B) photocells electrolysis fuels cells motor kinetic energy. C) electrolysis fuel cells photocells motor kinetic energy.
Answer: B
12) Compared with falling on a wooden floor a wine glass may not break when it falls on a carpeted floor because of A) lesser impulse in stopping. B) longer time to stop. C) both of these D) none of the above
Answer: B
13) From the edge of a roof you throw a snowball downward that strikes the ground with 100 J of kinetic energy. Then you throw a second snowball upward with the same initial speed and this too falls to the ground. Neglecting air resistance the second snowball hits the ground with a kinetic energy of A) less than 100 J. B) 100 J. C) 200 J. D) more than 200 J. E) none of the above
Answer: B
14) A 2-kg mass that weighs 20 N has 40 J of potential energy relative to the ground. What is its height? A) 1 m B) 2 m C) 3 m D) 4 m E) none of the above
Answer: B
14) According to the impulse-momentum relationship Ft = change in mv a falling baseball hits a player with a force F. The t in the equation is the time A) the ball falls before hitting the player. B) of contact of the ball hitting the player. C) of reflex as the player responds to being hit. D) all of the above E) none of the above
Answer: B
14) Compared to a recoiling rifle the bullet that is fired has a greater A) momentum. B) kinetic energy. C) none of the above
Answer: B
14) What is the mass of a ball moving at 4 m/s with a momentum of 48 kg∙m/s? A) 4 kg B) 12 kg C) 48 kg D) 192 kg E) none of the above
Answer: B
15) When a boxer is moving away from a punch the force experienced is reduced because A) momentum transfer is reduced. B) the time of contact is increased. C) the force is less effective. D) all of the above
Answer: B
16) When a boxer moves into an oncoming punch the force experienced is A) decreased. B) increased. C) no different but the timing is different. D) all of the above
Answer: B
17) A straw is used for a pea shooter. When you blow through the straw the speed of the emerging pea will be greater if the straw is A) cut in half. B) full length. C) either cut in half or full length.
Answer: B
17) Acrobat Bart at the circus drops vertically onto the end of a see-saw with his partner Art equidistant from the fulcrum at the other end. Art is propelled straight upward a distance twice that of Bart's dropping distance. Neglecting inefficiencies we see A) the masses of Art and Bart are equal. B) Art has half the mass of Bart. C) need more information
Answer: B
18) A 1000-kg truck moving at 10 m/s that brakes to a stop in 5 s has an average braking force of A) 1000 N. B) 2000 N. C) 3000 N. D) 4000 N. E) 5000 N.
Answer: B
18) An astronaut floating alone in outer space throws a baseball. If the ball moves away at 20 m/s the astronaut will move in the opposite direction at A) 20 m/s. B) a lower speed. C) a higher speed. D) more information needed E) none of the above
Answer: B
18) If a charging rhinoceros has momentum it must also have A) potential energy. B) kinetic energy. C) work. D) all of the above
Answer: B
19) A popular swinging-balls apparatus (Newton's cradle) consists of a series of identical elastic balls suspended by strings so they barely touch each other. When two balls are pulled away from one end and released they strike the row of balls and two balls pop out from the other end. If instead one ball popped out with twice the speed this would violate the conservation of A) momentum. B) energy. C) both of these D) none of the above
Answer: B
19) Work is done by gravity on a bowling ball that rolls A) along a horizontal surface. B) on a sloped surface. C) both of these D) none of the above
Answer: B
2) The impulse-momentum relationship is a direct result of A) Newton's first law. B) Newton's second law. C) Newton's third law.
Answer: B
2) Which of the following has the largest momentum relative to Earth? A) a tightrope walker crossing Niagara Falls B) a pickup truck speeding along a highway C) a Mack truck parked in a lot D) a dog running down the street
Answer: B
20) A cannonball fired from a long-barrel cannon will have a greater muzzle velocity because the cannonball receives a greater A) force. B) impulse. C) both of these D) none of the above
Answer: B
20) Whether a truck comes to a stop by crashing into a haystack or a brick wall the stopping force is A) greater with the haystack. B) greater with the brick wall. C) both the same
Answer: B
21) A blob of material in outer space moves at 3 m/s when it collides and sticks to a half-as-massive blob initially at rest. Compared with the initial kinetic energy of the 3-m/s blob the kinetic energy of the coupled blobs is A) one-third. B) two-thirds. C) three-quarters. D) not enough information
Answer: B
23) A karate chop is more effective if one's hand A) follows through upon impact. B) bounces upon impact. C) extends the time upon impact.
Answer: B
23) Which has greater kinetic energy: a car traveling at 30 km/h or another car of half the mass traveling at 60 km/h? A) The 30-km/h car B) The 60-km/h car C) both have the same kinetic energy
Answer: B
24) Just after a big fish swallows a small fish the momentum of the two-fish system is A) greater after lunch than before. B) the same before and after lunch. C) somewhat less after lunch.
Answer: B
24) The force of air impact upon the sail of a boat is greater if the air A) bounces upon impact. B) encounters the sail head-on. C) encounters the sail at a grazing angle.
Answer: B
25) A cat and a mouse run along a road with the same kinetic energy. The faster runner is the A) cat. B) mouse. C) both run at the same speed D) not enough information
Answer: B
28) A 1-kg chunk of putty moving at 1 m/s collides and sticks to a 5-kg bowling ball initially at rest. The bowling ball and putty move with a momentum of A) 0 kg∙m/s. B) 1 kg∙m/s. C) 2 kg∙m/s. D) 5 kg∙m/s. E) more than 5 kg∙m/s.
Answer: B
3) The distinction between impulse and force involves the A) distance the force acts. B) time the force acts. C) difference between acceleration and velocity. D) mass and its effect on resisting a change in momentum.
Answer: B
3) When Jean standing on slippery ice catches her leaping dog Daisy the momentum of both Jean and Daisy after the catch is A) greater than their combined momentum before the catch. B) equal to their combined momentum before the catch. C) somewhat less than their combined momentum before the catch.
Answer: B
3) When you ride your scooter you have momentum. When you ride twice as fast you have A) almost twice the momentum. B) twice the momentum. C) four times the momentum. D) none of the above
Answer: B
31) Using 1000 J of work a toy elevator is raised from the ground floor to the second floor in 20 s. How much power does the elevator use? A) 20 W B) 50 W C) 100 W D) 1000 W E) 20000 W
Answer: B
33) When an apple falls to the ground momentum is transferred to the ground. The momentum absorbed by the ground is A) negligible compared to the momentum of the apple. B) greater if the apple bounces. C) greater than that of the apple whether or not bouncing occurs. D) none of the above
Answer: B
4) A freight train rolls along a track with considerable momentum. If it rolls at the same speed but has twice as much mass its momentum is A) zero. B) doubled. C) quadrupled. D) unchanged.
Answer: B
4) A hydraulic press like an inclined plane is capable of increasing energy. A) sometimes true B) always false C) always true D) sometimes false
Answer: B
4) Suppose a miracle car has a 100% efficient engine and burns fuel having an energy content of 40 MJ/L. If all resistant forces on this car traveling at highway speeds is 1000 N what is the overall limit in distance per liter driven on the highway? A) 30 km B) 40 km C) 50 km D) more than 50 km E) not enough information
Answer: B
4) The bob of a simple pendulum has its maximum kinetic energy at the A) top of its swing. B) bottom of its swing. C) midpoint between top and bottom of its swing. D) at all points along its path of swing.
Answer: B
40) An open freight car rolls friction-free along a horizontal track in vertically pouring rain. As water accumulates in the car its speed A) increases. B) decreases. C) doesn't change.
Answer: B
6) What is produced by the process of electrolysis? A) energy B) hydrogen and oxygen C) pure drinking water D) photovoltaic power
Answer: B
7) A block of ice sliding down an incline has one-quarter its maximum potential energy A) one-quarter from the top. B) one-quarter from the bottom. C) three-quarters the way down. D) need more information
Answer: B
7) A car that travels twice as fast as another car when braking to a stop will skid A) twice as far. B) four times as far. C) depends on the mass of the cars.
Answer: B
7) Consider a gun with a pellet that is more massive than the gun. The firing speed is greater for the A) pellet. B) recoiling gun. C) both are the same D) none of the above
Answer: B
9) When a simple machine multiplies force it decreases A) potential energy. B) distance moved. C) both of these D) none of the above
Answer: B
3) A boy fires a spring-loaded Ping-Pong ball gun. Briefly compare the forces and impulses on the gun and the ball. Which has more momentum? Which moves faster?
Answer: Both force and impulse on both the ball and the gun are equal and opposite. So they both undergo equal and opposite changes in momentum. Since they begin with no momentum they have equal and opposite momentum as the ball fires and the gun recoils. Because the ball is less massive it has the greater acceleration for the same force and therefore moves faster.
1) A common pulley acts similar to a A) hydraulic press. B) gear. C) common lever. D) tension producer.
Answer: C
1) The conservation of momentum is most closely related to Newton's A) first law. B) second law. C) third law.
Answer: C
1) Which has the greater momentum when moving? A) a container ship B) a bullet C) either of these depending on speed
Answer: C
1) Which of these forms of energy is not renewable? A) wind power B) solar power C) fossil fuel power D) photovoltaic power
Answer: C
10) A 5000-kg freight car crashes into a 10000-kg freight car at rest. They couple upon collision and move with a speed of 2 m/s. What was the initial speed of the 5000-kg freight car? A) 4 m/s B) 5 m/s C) 6 m/s D) 8 m/s E) none of the above
Answer: C
10) When the input piston of a hydraulic press is depressed 20 cm the output piston is observed to move 1 cm. An input force of 1 N can raise no more than A) 1 N. B) 10 N. C) 20 N. D) 21 N.
Answer: C
11) Padded dashboards in cars are safer in an accident than non-padded ones because a person hitting the dash has A) increased time of contact. B) decreased contact force. C) both of these D) neither of these
Answer: C
12) What is the speed of a 6-kg ball with a momentum of 72 kg∙m/s? A) 3 m/s B) 4 m/s C) 12 m/s D) 48 m/s E) none of the above
Answer: C
13) What is the mass of a ball moving at 3 m/s with a momentum of 48 kg∙m/s? A) 4 kg B) 12 kg C) 16 kg D) 144 kg E) none of these
Answer: C
13) While driving down the highway a lovebug spatters onto your windshield. Which undergoes the greater impulse? A) the lovebug B) your car C) both the same
Answer: C
14) While driving down the highway a lovebug spatters onto your windshield. Which undergoes the greater change in momentum during the time of contact? A) the lovebug B) your car C) both the same
Answer: C
15) While driving down the highway a lovebug spatters onto your windshield. Which experiences the greater force of impact? A) the lovebug B) your car C) both the same but with different consequences
Answer: C
16) A bow is drawn so that it has 40 J of potential energy. When the arrow is fired its kinetic energy is ideally A) less than 40 J. B) more than 40 J. C) 40 J.
Answer: C
17) A boxer punches a sheet of paper in midair from rest to a speed of 40 m/s in 0.05 s. If the mass of the paper is 0.01 kg the force of the punch on the paper is A) 0.08 N. B) 0.8 N. C) 8.0 N. D) 80 N.
Answer: C
19) Whether a truck comes to a stop by crashing into a haystack or a brick wall the impulse is A) greater with the haystack. B) greater with the brick wall. C) both the same
Answer: C
2) A jack system will increase the potential energy of a heavy load by no more than 1000 J with a work input of 2000 J. The efficiency of the jack system is at most A) 10%. B) 20%. C) 50%. D) 80%. E) not enough information
Answer: C
2) A pulley system can A) change the direction of a force. B) multiply a force. C) both of these D) none of the above
Answer: C
20) A melon is tossed straight upward with 100 J of kinetic energy. If air resistance is negligible the melon will return to its initial level with a kinetic energy of A) less than 100 J. B) more than 100 J. C) 100 J. D) need more information
Answer: C
20) A piece of taffy slams into and sticks to another identical piece of taffy at rest. The momentum of the two pieces of taffy stuck together after the collision is the same as it was before the collision. Kinetic energy is a different story for part of it turns into heat. What percentage of the kinetic energy converts into heat? A) 0% B) 25% C) 50% D) 75% E) not enough information
Answer: C
21) A 2-kg rifle is horizontally suspended by a pair of strings so that recoil can be measured. The rifle fires a 0.001-kg bullet at a speed of 200 m/s. The recoil velocity of the rifle is about A) 0.001 m/s. B) 0.01 m/s. C) 0.1 m/s. D) 1 m/s. E) none of the above
Answer: C
21) Which of these two collisions is more damaging driving into a concrete wall with no "give" or colliding head-on with an identical car moving toward you at your same speed? A) collision with the car B) collision with the wall C) both the same
Answer: C
22) A 5-kg fish swimming at a speed of 1 m/s swallows an absent-minded 1-kg fish at rest. The speed of the larger fish after lunch is A) 1/2 m/s. B) 2/5 m/s. C) 5/6 m/s. D) 6/5 m/s. E) 1 m/s.
Answer: C
23) A 5-kg fish swimming at 1 m/s swallows an absent-minded 1-kg fish swimming toward it at 4 m/s. The speed of the larger fish after lunch is A) 1/2 m/s. B) 1/5 m/s. C) 1/6 m/s. D) 2/3 m/s. E) 3/2 m/s.
Answer: C
24) A shopping cart moves with a kinetic energy of 40 J. If it moves at twice the speed its kinetic energy is A) 40 J. B) 80 J. C) 160 J. D) not enough information
Answer: C
25) The total momentum of a flock of identical birds could be zero only if the birds are A) taking off from the ground. B) flying in the same direction. C) flying in different directions. D) very tired and coming down to rest.
Answer: C
26) A 1-kg chunk of putty moving at 1 m/s collides and sticks to a 5-kg bowling ball that is initially at rest in space. The bowling ball and putty are then set in motion with a speed of A) 1/4 m/s. B) 1/5 m/s. C) 1/6 m/s. D) none of the above E) not enough information
Answer: C
27) You do work on a cart loaded with groceries. If you do this work in one-third the usual time you expend A) one third as much power. B) the usual power. C) three times the usual power. D) need more information.
Answer: C
28) If you do work on an object in half the time your power output is A) half. B) the same. C) twice.
Answer: C
29) A piece of putty moving with 1 unit of momentum strikes and sticks to a heavy bowling ball initially at rest. After the putty sticks to the ball both move with a combined momentum of A) less than 1 unit. B) more than 1 unit. C) 1 unit. D) not enough information
Answer: C
29) If you exert 6 N across a distance of 2 m in 3 s you'll deliver a power of A) 1 W. B) 3 W. C) 4 W. D) 6 W. E) more than 6 W
Answer: C
3) A pulley has two supporting strands. To lift a load 1 meter means you will have to pull a distance of A) 1/2 m. B) 1 m. C) 2 m. D) more than 2 m.
Answer: C
3) No work is done by gravity on a bowling ball that rolls along a bowling alley because A) no force acts on the ball. B) no distance is covered by the ball. C) the force on the ball is at right angles to its motion. D) no potential energy converts to kinetic energy. E) its kinetic energy may vary.
Answer: C
3) The source of Earth's internal energy involves A) kinetic energy. B) potential energy. C) radioactivity. D) the Sun.
Answer: C
30) If you exert 100 J to lift a box in 50 s your power output is A) 1/4 W. B) 1/2 W. C) 2 W. D) 4 W. E) more than 4 W.
Answer: C
31) A 30-kg girl on friction-free roller blades pushes away a 25-kg boy also on roller blades at 1 m/s. The girl's speed is A) 0.45 m/s. B) 0.55 m/s. C) 0.83 m/s. D) 1.2 m/s.
Answer: C
32) Which requires more work: lifting a 50-kg sack vertically 2 m or lifting a 25-kg sack vertically 4 m? A) lifting the 50-kg sack B) lifting the 25-kg sack C) both require the same amount of work Answer: C Diff: 2 Topic: Energy and Work 33) A 50-kg sack is lifted 2 m in the same time as a 25-kg sack is lifted 4 m. The power expended in raising the 50-kg sack compared to the power used to lift the 25-kg sack is A) twice as much. B) half as much. C) the same.
Answer: C
35) Consider gliders that slide friction-free along a horizontal air track. Glider A has a mass of 1 kg a speed of 1 m/s and collides with glider B which has a mass of 5 kg and is at rest. If they stick upon collision the combined-glider speed will be A) 1/4 m/s. B) 1/5 m/s. C) 1/6 m/s. D) 1 m/s. E) none of the above
Answer: C
36) A 1-kg glider and a 2-kg glider both slide toward each other at 1 m/s on an air track. When they collide and stick the combined-glider speed is A) 0 m/s. B) 1/2 m/s. C) 1/3 m/s. D) 1/6 m/s. E) 1.5 m/s.
Answer: C
4) Jogging Jake runs along the top of a moving flatcar in the direction of motion of the flatcar. If he runs in the opposite direction the combined momentum of Jake and the flatcar relative to an observer at rest will be A) more. B) the same. C) less.
Answer: C
5) After rolling half-way down an incline a marble's kinetic energy is A) less than its potential energy. B) greater than its potential energy. C) the same as its potential energy.
Answer: C
5) An object in motion is an object that has A) acceleration. B) impulse. C) momentum. D) all of the above E) none of the above
Answer: C
5) Solar power is commonly used to produce A) heat. B) electricity. C) both of these
Answer: C
6) A block of ice sliding down an incline has half its maximum kinetic energy A) at the top. B) at the bottom. C) half-way down. D) need more information
Answer: C
6) To catch a fast-moving softball with your bare hand you extend your hand forward just before the catch and then let the ball ride backward with your hand. Doing this reduces the catching force because the A) relative velocity is less. B) relative velocity is more. C) time of catch is increased. D) time of the catch is decreased. E) none of the above
Answer: C
6) When a cannon fires a cannonball at a given speed the smaller recoil speed of the cannon is due to differences in A) forces. B) times. C) masses. D) momenta.
Answer: C
7) A karate expert executes a swift blow and breaks a cement block with her bare hand. The magnitude of the force on her hand is A) zero. B) less than the force applied to the cement block. C) the same as the force applied to the block. D) more than the force applied to the block. E) need more information
Answer: C
7) A simple machine cannot multiply A) force. B) distance. C) energy. D) none of the above
Answer: C
7) An iron ball and wooden ball of the same size are dropped simultaneously from a tower and reach the ground at the same time. The iron ball has a greater A) speed. B) acceleration. C) momentum. D) all of the above E) none of the above
Answer: C
7) The exhaust product from a hydrogen fuel cell is A) carbon dioxide. B) methane. C) pure water. D) nitric acid.
Answer: C
8) A 1000-kg car and a 2000-kg car are hoisted the same vertical distance in a service station. Raising the more massive car requires A) less work. B) as much work. C) twice as much work. D) four times as much work. E) more than four times as much work.
Answer: C
8) When you jump from an elevated position you usually bend your knees upon reaching the ground. By doing this the contact time is about 10 times more than for a stiff-legged landing and the average force your body experiences is reduced by A) less than 10 times. B) more than 10 times. C) about 10 times.
Answer: C
8) Which of these is not a form of solar energy? A) wind energy B) fossil fuel energy C) geothermal energy D) hydroelectric power
Answer: C
9) A heavy truck and a small truck roll down a hill. Neglecting friction at the bottom of the hill the heavy truck has greater A) speed. B) acceleration. C) momentum. D) all of the above E) none of the above
Answer: C
9) An object lifted 10 m gains a certain amount of potential energy. If it is lifted 20 m its gain in potential energy is A) less. B) the same. C) twice as much. D) four times as much. E) more than four times as much.
Answer: C
9) Two identical arrows one with twice the speed of the other are fired into a bale of hay. The faster arrow will penetrate the bale A) the same distance as the slower arrow. B) twice as far as the slower arrow. C) four times as far as the slower arrow. D) more than four times as far as the slower arrow. E) none of the above
Answer: C
Diff: 2 39) When Freddy Frog drops vertically from a tree onto a horizontally-moving skateboard he doesn't slip off the skateboard because of A) inertia in motion. B) momentum change. C) friction between his feet and the board.
Answer: C
10) A boulder is dropped onto mud and plows into it a certain distance. If it hits with three times as much speed the distance it plows into the mud will likely be A) the same distance. B) twice as deep. C) three times as deep. D) more than three times as deep.
Answer: D
10) A car traveling along the highway brakes to a stop. A greater braking force is required when the car has A) more mass. B) more momentum. C) less stopping distance. D) all of the above E) none of the above
Answer: D
10) A music console is pushed 2 m by a force of 20 N. The work done on the console is A) 2 J. B) 10 J. C) 20 J. D) 40 J. E) 80 J.
Answer: D
13) A 2-kg mass weighs 20 N and is held 4 m above the ground. Its potential energy relative to the ground is A) 8 J. B) 20 J. C) 60 J. D) 80 J. E) none of the above
Answer: D
16) A circus diver drops from a high pole into water far below. When he is half-way down A) his potential energy is halved. B) he has gained an amount of kinetic energy equal to half his initial potential energy. C) his kinetic and potential energies are equal. D) all of the above E) none of the above
Answer: D
2) The most energy per unit mass can be extracted from A) coal. B) petroleum. C) natural gas. D) uranium.
Answer: D
22) The massive ram of a pile driver falling from rest strikes a pile with a speed that depends on the A) initial height of the ram. B) initial potential energy of the ram. C) distance the ram falls. D) all of the above
Answer: D
26) Power is defined as the A) force exerted divided by the time of exertion. B) force exerted multiplied by the distance moved. C) work done multiplied by the time to do the work. D) work done divided by the time to do the work. E) none of the above
Answer: D
27) A 0.5-kg blob of clay moving at 2.0 m/s slams into a 4.0-kg blob of clay at rest. The speed of the two blobs stuck together after colliding is about A) 1.1 m/s. B) 1.5 m/s. C) 2.5 m/s. D) none of the above
Answer: D
3) A ball rolling down an incline has its maximum kinetic energy at A) the top. B) half-way down. C) three-quarters of the way down. D) the bottom.
Answer: D
3) If a power plant is 30% efficient and the transmission system that delivers power to consumers is 60% efficient then the overall efficiency is A) 90%. B) 60%. C) 30%. D) 18%. E) none of the above
Answer: D
32) When a 100-kg astronaut ejects 0.1 kg of gas at a speed of 50 m/s from her propulsion pistol her recoil speed is A) 50 m/s. B) 5.0 m/s. C) 0.5 m/s. D) 0.05 m/s.
Answer: D
34) The power expended for a barbell raised 2.0 m in 2 s is A) 1 W. B) 4 W. C) 8 W. D) not enough information
Answer: D
4) A car moves 4 times as fast as another identical car. Compared with the slower car the faster car has A) 4 times the kinetic energy. B) 8 times the kinetic energy. C) 12 times the kinetic energy. D) 16 times the kinetic energy.
Answer: D
4) When Peter tosses an egg against a sagging sheet the egg doesn't break due to A) reduced impulse. B) reduced momentum. C) both of these D) neither of these
Answer: D
5) A common car engine is 20% efficient. When cruising the car encounters an average retarding force of 1000 N. If the energy content of gasoline is 40 MJ/L how many kilometers per liter does the car achieve? A) 14 km/L B) 12 km/L C) 10 km/L D) 8 km/L E) none of the above
Answer: D
5) The force of a falling apple hitting the ground depends upon A) the speed of the apple just before it hits the ground. B) the time of contact with the ground. C) whether or not the apple bounces. D) all of the above
Answer: D
5) The force that accelerates a rocket in outer space is exerted on the rocket by the A) rocket's engine. B) rocket's wings. C) atmospheric pressure. D) exhaust gases. E) none of the above
Answer: D
6) A car moving at 50 km/h skids 20 m with locked brakes. How far will it skid if its initial speed is 150 km/h? A) 20 m B) 60 m C) 90 m D) 180 m
Answer: D
6) A hydraulic jack is used to lift an automobile. If the input force is 200 N over a distance of 1 meter the output force over a distance of 0.1 meter is ideally A) 200 N. B) 500 N. C) 1000 N. D) 2000 N. E) none of the above
Answer: D
6) An object may have potential energy because of its A) speed. B) acceleration. C) momentum. D) location. E) none of the above
Answer: D
6) The change in momentum of an object is equal to the A) force acting on it. B) change in its velocity. C) object's mass times the force acting on it. D) impulse that acts on it. E) all of the above
Answer: D
7) The amount of potential energy possessed by an elevated object is A) relative to a chosen reference level. B) equal to the work done in lifting it. C) equal to the kinetic energy it will acquire when freely falling to its reference level. D) all of the above
Answer: D
8) The speed of a bullet fired from a gun will be about the same as the speed of the recoiling gun A) when momentum is conserved. B) because velocity is conserved. C) when both velocity and momentum are conserved. D) if the masses of the bullet and gun are equal. E) none of the above
Answer: D
9) When Danny Diver who weighs 500 N steps off a diving board 10 m above the water he hits the water with kinetic energy of A) 10 J. B) 500 J. C) 510 J. D) 5000 J. E) more than 5000 J.
Answer: D
12) A 1-kg ball dropped from a height of 2 m rebounds only 1.5 m after hitting the ground. The amount of energy converted to heat is about A) 0.5 J. B) 1.0 J. C) 1.5 J. D) 2.0 J. E) more than 2.0 J.
Answer: E
12) A sandbag is motionless in outer space. A second sandbag with 3 times the mass moving at 12 m/s collides with it and they both stick together and move at a speed of A) 3 m/s. B) 4 m/s. C) 6 m/s. D) 8 m/s. E) none of the above
Answer: E
15) A moving object has A) speed. B) velocity. C) momentum. D) energy. E) all of the above
Answer: E
2) When a bus brakes to a stop its kinetic energy transforms to A) stopping energy. B) potential energy. C) energy of motion. D) energy of rest. E) heat.
Answer: E
34) A 1-N-falling apple hits the ground with a force of A) 1 N. B) 2 N. C) 4 N. D) 10 N. E) not enough information
Answer: E
10) Give two explanations of why a cannonball fired from a long-barrel cannon will have a greater velocity than from a shorter cannon.
Answer: In terms of impulse-momentum the longer barrel means the time during which the exploding powder pushes on the cannonball is longer. This means more impulse which in turn means more gain in momentum and greater velocity. In terms of work-energy the longer barrel means a longer distance for the force to act which means greater work on the ball inside the barrel and more gain in kinetic energy and greater velocity.
4) A diesel locomotive coasting at 10 km/h has an inelastic collision with a stationary flatcar. The locomotive weighs four times as much as the flatcar. How fast does the locomotive-flatcar combination move when stuck together?
Answer: Momentum before collision = momentum after collision. masslocomotive × 10 km/h. = (masslocomotive + massflatcar) × v. So v = masslocomotive /(masslocomotive + massflatcar) × 10 km/h. Or v = 4 massflatcar/(4 + 1) massflatcar × 10 km/h = 8 km/h. So the coupled cars move at 8 km/h.
1) In terms of momentum why is a drinking glass less likely to break if it falls on a carpeted floor than falling on a hard concrete floor?
Answer: The carpeted floor has more "give" which means it takes more time for the momentum of the falling glass to reduce to zero as it hits the surface. More time means less force which means less chance of breaking upon contact with the carpeted floor.
7) Discuss how energy conservation applies to a swinging pendulum. Where is potential energy the most? Where is it the least? Where is kinetic energy the most? Where is it the least? Where is the pendulum bob moving fastest? Where is it the slowest?
Answer: The swinging pendulum has the most gravitational potential energy at the top of its swing. It has the most kinetic energy at the bottom of its swing where its potential energy is at a minimum. Halfway down it has half kinetic and half potential energy. Ideally everywhere along the swing the sum of the kinetic and potential energies is the same. When air resistance and friction are taken into account kinetic energy is transferred from the pendulum to the surrounding space as thermal energy. So the pendulum moves fastest at the bottom of its swing and slowest when it is highest.
5) Work is done on an object when you lift it against gravity. How does this work relate to gravitational potential energy? If the lifted object is dropped what becomes of this energy?
Answer: The work you do on the lifted object may be stored as gravitational potential energy. Then force × distance = weight × height. If the lifted object is dropped this energy transforms to motion energy—kinetic energy. The kinetic energy it possesses as it returns to its initial position equals the gravitational potential energy at its highest point which equals the initial work done.
8) Why does the force of gravity do no work on a bowling ball rolling along a bowling lane? Look ahead to the next chapter and apply your explanation to satellite motion.
Answer: Work is done on an object only when a force, or some component of a force, acts in the direction of motion of the object. In the case of the bowling ball, the force of gravity is perpendicular to the motion with no component parallel to the lane. We will see in the next chapter that, for the same reason, the force of gravity does no work on satellites in circular orbit. Diff: 2 Topic: Energy and Work 9) Can an object have mechanical energy without having momentum? Can an object have momentum without having mechanical energy? Explain., Answer: An object can have potential energy without moving which means it can have mechanical energy without having momentum. But if its mechanical energy is kinetic then it also has momentum. Any object with momentum also has kinetic energy. (All objects also have "energy of being" or mass energy E = mc2.)
25) A fan attached to an ice sailcraft stalled on a windless day blows air into the sail that bounces backward upon impact. The boat A) moves in the direction of the wind impact force. B) does not move by this wind impact. C) moves
but in the opposite direction of the wind impact force., Answer: A
5) When a hydraulic press is properly used it is capable of multiplying force input. A) true B) false C) true only in special cases
energy as well, Answer: A
8) Strictly speaking if any electrical device in an automobile is turned on (such as an air conditioner or even headlights) more fuel is consumed by the engine. This statement is A) true. B) true only if the engine is running. C) always false. D) sometimes true
sometimes false., Answer: A
5) When you push an object a certain distance while applying twice the force
you do A) twice as much work. B) four times as much work. C) the same amount of work., Answer: A
